Generally, in stores like supermarkets or convenience stores, selling prices of products in the stores are controlled collectively by a product master stored in a POS system and the like. Meanwhile, in many cases, a customer (consumer) is informed of selling prices by shelf labels formed from paper media arranged, in the positions of products. When such shelf labels of paper media are employed, the shelf labels should be controlled manually. In this case, human errors such as mistakes in selling prices are likely to occur. As a result, a customer may be informed of an incorrect selling price different from that at the time of payment by a cash register of a POS system.
In order to solve this problem, an ESL system (electronic shelf label system) has been put into active use in recent years as disclosed in Patent Documents 1 and 2. In the electronic shelf label system, a portable electronic shelf label for displaying product data relating to a product such as data indicative of a selling price is arranged in corresponding relation to each product. A communication signal containing data indicative of a selling price which is based on a product master is output from a distribution device for distributing information to each electronic shelf label. Then the selling price is displayed on each electronic shelf label. As a result, a correct selling price coinciding with a selling price at the time of payment is displayed on an electronic shelf label, by which a customer is informed of the correct selling price.
Patent Document 3 discloses a technique relating to a portable device, and Patent Document 4 discloses a technique relating to a camera.
Patent Document 1: Japanese Patent Publication No. 2002-516430
Patent Document 2: Japanese Patent Application Laid-Open No. 2001-5872
Patent Document 3: Japanese Patent Application Laid-Open No. 2003-189485
Patent Document 4: Japanese Patent Application Laid-Open No. 10-73866
As disclosed in Patent Document 1 cited above, in an electronic shelf label, generally, a to-be-charged part formed from a capacitor is charged by power supplied from a battery, and a transmission part formed from an LED sends data to a higher-order distribution device by using power given to the to-be-charged part. The internal resistance of a battery normally increases during operation in a low-temperature environment, or on the occurrence of performance degradation generated by change over time and the like. In a condition where the internal resistance is on the increase, the supply of a large amount of power from the battery to the to-be-charged part causes the output voltage of the battery to drop, so the electronic shelf label may not be in normal operation.